This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-24624 filed on Feb. 2, 2000, 2000-29909 filed on Feb. 8, 2000, 2000-29910 filed on Feb. 8, 2000, and 2000-388900 filed on Dec. 21, 2000.
1. Field of the Invention
The present invention relates to an installation structure of a printed-circuit board on which electronic devices are mounted, suitable for use in an electronic control unit of a vehicle engine.
2. Description of Related Art
An intake module of an internal combustion engine includes sub-modules such as an air cleaner, an intake duct, an air-flow sensor, a throttle body, and an intake manifold. The sub-modules include not only miscellaneous sensors and actuators, but also ECU (Electronic Control Unit), which has been installed in a vehicle cabin so far. Here, housings of the sub-modules are mainly made of resin.
The ECU is installed in a casing within an air cleaner made of resin. Since the casing is influenced by an engine vibration, a printed-circuit board disposed in the ECU is also influenced by the vibration. A resonance of the vibration might cause a vibration ten times as large as the engine vibration in the printed-circuit board. The large vibration worsens the electronic devices mounted on the printed-circuit board, so that the ECU does not work effectively.
An object of the present invention is to improve anti-stress and anti-vibration performance of an electronic control unit, and to reduce a total weight thereof.
According to a first aspect of the present invention, a printed-circuit board is fixed to a high rigid metal plate at a peripheral end and approximate center portions thereof. The metal plate includes a convex for containing a plurality of electronic devices mounted on a printed-circuit board. The printed-circuit board is contained in a casing. Thus, the resonance frequency of the printed-circuit board increases, and vibration amplitude at the resonance decreases, thereby preventing the electronic devices from being broken.
According to a second aspect of the present invention, the metal plate is fixed to the printed-circuit board at a side where an outside connector is attached to the printed-circuit board, so that a space defined by the printed-circuit board and an inner wall of the casing is set larger than the disposing dimension of the outside connector. Thus, the convex of the metal plate is easily and freely formed even when the shape thereof is complicated.
According to a third aspect of the present invention, an inside of the casing communicates with an intake air passage at some locations of the inner wall, and the metal plate covers the communicating locations for separating the printed-circuit board from the intake air passage. Thus, the metal plate faces the intake air passage, so that heat radiation of the electric devices is improved.
According to a fourth aspect of the present invention, a support member tightly pinches the printed-circuit board and the metal plate at plural peripheral ends thereof. Thus, the heat radiation of the electric devices is improved without worsening a mount efficiency of the printed-circuit board. The metal plate fixed to the printed-circuit board improves the anti-stress and anti-vibration performances of the ECU.
According to a fifth aspect of the present invention, the metal plate is provided on the printed-circuit board at an opposite side of the outside connector. Thus, the convex of the metal plate contains the electronic devices without being influenced by the outside connector, and covers most of the printed-circuit board. Thereby, the shape of metal plate is simplified, and heat radiation thereof is improved.
According to a sixth aspect of the present invention, an elastic plate is provided on the metal plate at an opposite side of the printed-circuit board, and a support member tightly pinching the printed-circuit board and the metal plate at plural peripheral ends thereof while providing the elastic plate between the metal plate and the support member. Thus, heat radiation of the electric devices is improved without worsening a mount efficiency of the printed-circuit board. The metal plate including the elastic plate fixed to the printed-circuit board improves the anti-stress and anti-vibration performances of the ECU.
According to a seventh aspect of the present invention, the printed-circuit board is fixed to the metal plate at four or more peripheral end portions. Thus, the anti-stress and anti-vibration performances of the printed-circuit board are improved.